Conventionally, an engineering part, a semiconductor part and the like are generally cleaned with an ultrasonic cleaning apparatus.
FIG. 3 shows a schematic view of an example of a conventionally general ultrasonic cleaning apparatus.
As shown in FIG. 3, the conventionally general ultrasonic cleaning apparatus 101 is provided with a cleaning tank 102 that accommodates cleaning liquid 107 for cleaning an object to be cleaned 104, an ultrasonic wave transmitting tank 103 that accommodates transmitting water 108 for transmitting ultrasonic waves to the cleaning tank 102, a vibrating plate 105 which is placed at an outer wall surface of the ultrasonic wave transmitting tank 103 and superposes the ultrasonic waves on the transmitting water 108 with an ultrasonic wave transducer 109, for example, composed of a ceramic piezoelectric device, and the like. The object to be cleaned 104 is held in the cleaning tank 102 with a holding jig 106 and the like, and immersed in the cleaning liquid accommodated in the cleaning tank 102. The cleaning tank 102 is put into the transmitting water 108 accommodated in the ultrasonic wave transmitting tank.
The ultrasonic waves superposed with the vibrating plate 105 are transmitted to the cleaning tank 102 through the transmitting water 108 so that a standing wave bounded by a surface of the cleaning liquid 107, walls of the cleaning tank and the like is formed. In this case, the cleaning liquid that is into contact with the antinode of the standing wave greatly vibrates, and the object to be cleaned 104 is cleaned by sound pressure due to the vibration.
However, since waveform of the standing wave in the cleaning liquid 107 is determined by a shape of the cleaning tank 102, a placement position and frequency of the ultrasonic wave transducer 109, and a type, temperature, a depth and the like of the cleaning liquid 107, a position of the antinode and node of the standing wave does not change provided that these conditions are constant. Therefore, since the cleaning liquid 107 hardly vibrates at the position of the node of the standing wave, a portion of the object to be cleaned 104 located at the position of the node of the standing wave cannot be sufficiently cleaned. Thus, there is a problem that the whole of the object to be cleaned cannot be cleaned uniformly, unevenness of cleaning consequently occurs and the like.
In view of the problem as described above, there is disclosed an ultrasonic cleaning apparatus that can efficiently clean by oscillating a cassette accommodating a semiconductor part in two-dimensional manner (See Japanese Patent Laid-open (Kokai) No. H9-260334).
There is also disclosed a substrate cleaning apparatus that can sufficiently remove contaminated materials over the whole surface of a substrate by arranging a plurality of the substrates, which are the object to be cleaned, and a plurality of rod members provided with the ultrasonic wave transducer at an end portion of its one side in such a manner that each main surface of the substrates and the rod members are arranged oppositely in parallel to one another, and by cleaning the substrates ultrasonically while the substrates and the rod members are relatively moved parallel (See Japanese Patent Laid-open (Kokai) No. 2002-59095).
In recent years, the ultrasonic wave of a high frequency of 1 MHz is used in the ultrasonic cleaning of the object to be cleaned such as a semiconductor part, for example, for reasons of removing particles of a wafer effectively and improving particle quality. However, the higher the frequency of the used ultrasonic wave becomes, the stronger the directivity of the ultrasonic wave becomes, and thereby affecting the foregoing problem of the unevenness of cleaning greatly.
In view of the problems, as the disclosed substrate cleaning apparatus does, the cleaning is performed while varying the position where the object to be cleaned comes into contact with the node of the standing wave by oscillating the holding jig holding the object to be cleaned or by providing a plurality of the cleaning tanks, and varying the position of the holding jig in one of the cleaning tanks or changing the cleaning tank in which the holding jig is arranged during the cleaning. However, even though the cleaning is performed by the method as described above, there are still problems that a suppression effect on the unevenness of cleaning and a removal effect on the particles of the object to be cleaned are insufficient, and apparatus cost increases in the case of providing a plurality of the cleaning tanks.